Evaluating the effectiveness of EPA's proposed runoff mitigation plan on atrazine surface water concentrations in the...

Atrazine is the second most widely used pesticide and the most widespread pesticide water contaminant in the United States. As part of its periodic review of atrazine impacts, the US regulatory authority on pesticides-the Environmental Protection Agency (EPA)-is in the process of identifying atrazine risks and crafting a plan to mitigate atrazine runoff. EPA's review has found extensive atrazine water contamination in the United States, with over one-eighth of the watersheds in the continental United States estimated to contain atrazine concentrations exceeding levels known to harm aquatic ecosystems. EPA has crafted a runoff mitigation proposal that seeks to reduce the levels of atrazine in US waterways by 1) reducing the maximum annual application rate by 20% and 2) implementing a geographically specific, point-based mitigation system. Here, we assessed the efficacy of this plan using known regional application rate utilization and geospatial estimation of point attainment. Following implementation of this plan, we found that only 1% of the 11,248 contaminated watersheds in the United States would drop below the EPA-identified concentration that can harm aquatic ecosystems. We further confirmed this with a field-level analysis in a highly contaminated county in the most atrazine-contaminated state and found that this plan would fail to require any additional runoff mitigating practices from 100% of corn fields adjacent to surface water. If implemented, this runoff mitigation plan will likely have little quantifiable impact on current in-stream atrazine concentrations, many of which are currently above levels known to harm aquatic ecosystems.